USB communication transceiver using optical link

ABSTRACT

An optical version of USB is provided to enable PDAs and digital cameras to download data and media files to remote network servers. The PDA is plugged into an optical transceiver that communicates with a complementary transceiver located in a network terminal (for example a payphone) that is in communication with the network server.

This application is the U.S. national phase of international applicationPCT/GB02/01037 filed 7 Mar. 2002 which designated the U.S.

BACKGROUND

1. Technical Field

The invention relates to optical communications links, in particularoptical free-space communications links for transmission over shortdistances.

2. Related Art

Recent advances in consumer electronics have led to the development ofmany different devices such as digital cameras, personal digitalorganisers, MP3 players, etc that are capable of exchanging datadirectly with personal computers (PCs) or over communications networks,for example, downloading data from World Wide Web (WWW) servers. Many ofthese use connectors complying with the USB standard.

A USB connection is a half-duplex communication, carried over two datawires. An additional two wires carry power. The two data wires do nothave a data flow direction associated with them, as the RS232 serialcommunication does, but the two wires give a differential signal whoserelative polarity defines a logic zero or one. Hence, the data must besent in a half-duplex fashion to prevent collisions on the connection,which of course would lead to data corruption.

Users of devices connected by a USB connection can use a connection to aPC (personal computer) or to a communications network to transfer datato or from their device (for example transferring digital camera imagefiles to a WWW server or synchronizing diary data held on a PDA(personal digital assistant) with that held on a PC). It is relativelyeasy for users to connect their devices to transfer data when in, forexample, their home or their workplace where there is access to acommunications network, for example using dial-up access over the PSTN(public switched telephone network) or access to a LAN (local areanetwork)(with an Internet gateway.

Several multi-wire schemes are available such as the standard PrinterParallel Bus and the IEEE488 GPIB Bus, hard-wired serial schemes such asthe RS232 Serial Bus, and optical serial schemes like the IrDA OpticalBus. These methods all require complex software control systems to allowdata transfer across the link with no intervention from the systemswhatsoever. Any error handling or flow control comes from theapplication software itself.

If users do not have such network access then the fallback option is toconnect using a mobile communications network. Whilst this may be anacceptable choice when sending short emails or synchronising a diaryfrom a PDA, the limited transmission capabilities (9.6 kb/s with a GSMmobile telephone network) make it impractical for exchanging largerquantities of data, for example uploading digital camera images ordownloading music files when the respective devices may have memory cardstorage capacities of 256 MB or even greater (very much greater fordevices having disk storage capabilities). Although GPRS and UMTS mobilecommunication networks promise to deliver greater transmission rates tomobile users they are not currently in use and it is not altogetherclear what data transmission rates will be available to users inpractice.

BRIEF SUMMARY

The present invention seeks to provide a means of sending and receivingdata across a link without the complexity of conversion to one of themultichannel systems discussed above.

According to a first aspect of the invention there is provided anoptical transceiver, the transceiver comprising means enabling anassociated electronic device to, in use, transmit and receive datasignals in the USB two channel format, and means to directly modulatethe received USB-format signals onto an optical carrier.

The use of an optical connection allows a publicly accessible hostterminal to provide connection to user equipment without making itvulnerable to damage, for example from bent electrical pins or wateringress. Because the USB format carries two parallel channels some formof docking port is desirable to ensure correct alignment of the opticalinterfaces to avoid interference between the channels, or from externallight sources. However, because the terminals in the port are opticalthey are much more easily protected from accidental or malicious damagethan electrical terminals could be.

In an electrical USB connection two way traffic is possible over asingle wire pair, but in an optical arrangement separate outward andreturn paths are required. The need for separate paths arises because anoptical link by definition can only work in one direction—there is anemitter and a detector, and they must be physically separated to someextent to prevent self-detection. Therefore, each of the two data wireshas to have an emitter and a detector to allow bi-directionalcommunication. In its simplest form the two data wires of the USB systemcould be replaced by two pairs of optical links that emulated the hardwired system.

It is desirable to have such a link operate in a manner that allowstransparent operation of the link as if a cable was still attacheddirectly. However, the need to protect the circuitry from locking upmeans that the signal would become unacceptably degraded. Locking up isillustrated in FIG. 4, and arises because without any directioninformation each optical pair 101, 311; 301, 111 has to be hard wired inreverse parallel, as shown in FIG. 4, which leads to a latchingsituation in which a signal from an input 191, for transmission over anoptical path 101, 311 to an output 391, can loop through the return path301, 111 one or more times. To prevent this “latching”, the transceiveris preferably arranged for time division duplex operation with aco-operating transceiver, that is to say that one transceiver is in atransmit only mode when the other is in a receive only mode. Thisrequires a method of detecting the intended direction of data flow inadvance of that flow itself. If this ‘foresight’ is not achieved thenthe data would start to flow before the link is turned around, thuslosing some of the data and corrupting the communication. To co-ordinatethe operation of two such transceivers, a first one preferably comprisesmeans for transmitting a control signal for controlling the operation ofa the co-operating transceiver, means for operating in receive mode fora predetermined period after transmission of the control signal, meansfor detecting signals received from the co-operating transceiver, andmeans for switching to transmit mode if no such signals are detected.The co-operating transceiver, and means for putting the transceiver intotransmit mode in response to the control signal.

In the USB system the data rate at which the connection is to beoperated is determined by detection of a physical configuration of theuser terminal, specifically by detecting to which signalling wire apull-up resistor is connected. This information can be carried acrossthe optical link by providing, in one of the transceivers, means fordetecting this configuration, means for generating data in accordancewith the detected configuration, means for detecting an idle period inthe transmitted and received data signals, and means for transmittingthe generated configuration data over the optical link during said idleperiod. The corresponding transceiver comprises means for detecting theidle periods in the transmitted and received data signals, means forreceiving configuration data over the optical link during said idleperiods, and means for configuring the electronic device according tothe configuration data, specifically by generating an electrical signalreplicating that which would have been detected by the terminal had itbeen connected directly to the user terminal.

Preferably a first transceiver comprises detection means for detectingan alert signal indicative that a co-operating transceiver is present,whilst the co-operating transceiver comprises transmission means fortransmitting an alert signal to the first transceiver indicative of itspresence. This arrangement ensures that spurious behavior is not causedby other light sources when no co-operating transceiver is present.

The transmission means are preferably pulsed light emitting diodes, andthe detection means are preferably optical sensors. In a preferredarrangement, each transceiver comprises three pairs of opticaltransmitters and sensors, wherein two of the pairs are used for duplexoperation in the two-channel USB format, and the third pair is used forexchange of the alert and control signals

The invention also extends to a communications terminal comprising atransceiver of the type described above, which may be connected to astorage device by a communications network, and may include means forprocessing payment for use of the terminal, such as a cash or creditcard payment system. The co-operating transceiver may also be of thetype described above, and may comprise means for connection to anddisconnection from an associated electronic device. Such a connectionmay be a standard wired USB format connection, allowing wired equipmentbuilt to this standard to interface with the optical transceiver in theterminal by connecting a USB-to-optical interface device incorporatingthe transceiver according to the invention between them.

In the described embodiment, the transceiver connected to the electronicdevice generates the alert and configuration signals, and receives thecontrol signal, whilst the co-operating transceiver connected to thecommunications network transmits the control signal, and responds to thealert signal and configuration signals. However, other permutations arepossible within the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic depiction of an arrangement incorporating adevice according to the present invention;

FIG. 2 shows a schematic depiction of the structure of a firsttransceiver suitable for use in the present invention;

FIG. 3 shows a schematic depiction of the structure of a secondtransceiver suitable for use in the present invention, and complementaryto the transceiver of FIG. 2; and

FIG. 4 shows a pair of non-optimal optical connectors, illustrating theproblem of latching, and has already been discussed.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 shows an arrangement incorporating a device according to anexemplary embodiment of the present invention including an opticaltransceiver 10 (hereinafter referred to as the peripheral transceiver),an electronic device 20, and a communications network terminal 40 whichincorporates a further optical transceiver 30 (hereinafter referred toas the host transceiver), the communications network terminal also beingconnected to a communications network 50. The optical peripheraltransceiver 10 is connected to the electronic device 20 by a cable 11which connects to a communications port 21 of the electronic device. Thecommunications port 21 and the cable 11 are arranged according to theUniversal Serial Bus (USB) communications link. Data transmission ratesof up to 12 Mb/s are possible under the USB 1.1 specification, and theUSB 2.0 specification envisages data rates of up to 480 Mb/s. USB portshave become ubiquitous in modem PCs, laptops and PDAs and are becomingcommon in devices such as digital cameras, MP3 players, etc.

The communications terminal 40 allows the user to make a connection to adesired information repository 52; for example a secure partition of theuser's WWW server, so that images from a digital camera might betransferred to the server to allow further images to be taken with thecamera, or downloading music files from a service such as myMP3.com orconnecting to an email server, etc. The communications terminal 40comprises a display screen 41, an input controller 42 (which may be akeyboard, mouse, trackball, or a touch screen facility incorporated inthe screen 41) and a card reader 43 that enables a user to insert acredit card, smart card or other payment card. The communicationsterminal 40 may additionally comprise a mechanism for accepting coins,as is known from conventional payphones. The communications terminal 40is connected to the communications network 50 by a communications link51, with the communications network 50 being in communication with theinternet such as a WWW server storage device (52). The communicationslink 51 may be a PSTN line, with the communications terminal 40 using amodem to communicate with an internet PoP (point of presence) but it isadvantageous for the communications link 51 to have an increased datatransmission capacity to facilitate rapid transfer of data to and fromthe electronic device 20, for example an ISDN or DSL connection or otherhigh-speed connection. As an alternative the communications link 51could be provided using a radio communications link or an optical fibrecommunications link. ADSL (asymmetric digital subscriber loop) could beused, although it is likely that there will be an approximately equalnumber of users who wish to upload data to a server as those who wish todownload data from a server and an asymmetric transmission system wouldhandicap one of these user groups. ADSL could be used to advantage if itwere possible to re-initialise the ADSL connection such that the higherdata rate connection could be aligned with the needs of the users.

When a user needs to transfer data to or from the electronic device 20then the transceivers 10, 30 in the device 20 and terminal 40 arealigned, and the user makes sufficient payment to enable use of thesystem (the payment may cover, for example a session of limitedduration, the transmission of a given volume of data or a single sessionwithout any such restriction). The user enters the address of the datarepository to be accessed using the input controller 42 and initiatesthe transfer of data between the data repository 52 and the electronicdevice 20. The electronic device 20 transmits data via its connector 21to the peripheral transceiver 10. The peripheral transceiver 10 convertsthe electrical USB signals into infra-red USB signals which are thentransmitted through free-space to the host transceiver 30 in theterminal 40, at which point the infra-red USB signals are converted backinto the electrical domain. The communications terminal 40 thentransmits the data via the communications link 51 to the communicationsnetwork 50, where the data is routed to the data repository 52. Data isrouted from the data repository 52 to the electronic device 20 by thereverse route.

It may be necessary for the terminal 40 to use device-specific driversin order to transmit data to and receive data from the electronicdevice. This can be achieved by a number of different methods. Forexample, the operator of the terminal 40 may decide only to support themost popular electronic devices and store the required drivers in theterminal 40, or on a server connected to a private network accessible bythe terminal 40. Alternatively, the terminal 40 may download the driversfrom the device 20, or from a remote network location which isidentified by the device 20, such as the website of either the user orthe device manufacturer, when the device begins communication with theterminal. This would ensure that the most up to date drivers are alwaysused. As a further alternative the dynamic proxy server architectureproposed by Fry and Ghosh would allow the terminal to access and executerequired device drivers as necessary.

In order to implement a preferred embodiment of the present invention,it is necessary to provide a transceiver that connects to an electronicdevice that can generate infra-red data signals from the electrical USBsignals created by the electrical device and generate electrical USBsignals from the infra-red data signals received from the terminaltransceiver. It is also necessary to provide a complementary transceiverfor use in the terminal. A pair of such transceivers 10, 30 are shown inFIGS. 2 and 3. The embodiment is arranged such that the terminal andperipheral operate as if connected directly together, in other words thedevice 20 and terminal 40 each co-operates with its respectivetransceiver 10, 30 in the same way that they would with each other ifconnected directly through the connection 11, 31, so neither the device20 nor the terminal 40 require any modification.

Standard USB links 11, 31 are provided between the terminal 40 anddevice 20 to their respective transceivers 10, 30. The USB specificationrequires USB link 11, 31 cables to have two wires 198, 199; (398, 399)to carry electrical power and two wires 191, 192; (391, 392) to carrythe data. The power connections 198, 199; 398, 399 provide power to therespective transceivers 10, 30 (and in particular the LEDs to bedescribed later), through respective power control systems 18, 38, whichwill not be described in detail. There are of course no powerconnections across the infra-red link.

The data wires 198, 199, (398, 399) are both bi-directional. The datawires operate on a differential basis, that is to say, the two wiresgenerally carry binary signals of opposite polarity, a logical “1” beingindicated by a first data wire being “high” and the other data wirebeing “low”, whilst for a logical “0” the first data wire is “low” andthe second data wire is “high”. Thus the data can be interpreted byexamining the differential state of the wires. In addition to this, avalid state exists where both wires are held Low, and this is called aSingle Ended Zero (SE0). Further formatting, known as Non Return to ZeroInvert format (NRZI), and “bit-stuffing” are used to ensure that someactivity happens on a regular basis, but for clarity purposes,everything that follows will assume that the NRZI encoding and bitstuffing do not exist, and all references to data will refer to the rawlogic state of that data. The general transmission of data involvessending what are known as PACKETS, each preceded by a Start Of Packet(SOP) signal and terminated by an End Of Packet (EOP) signal. The SOP ispurely the transition from the Idle state to a state known as theK-state. The EOP is signaled by the lines being put in the SE0 state for2 bit times followed by a transition to a state known as the J-state forone bit time. The USB 1.1 specification allows for two data rates(low-speed at 1.5 Mb/s and high-speed at 12 Mb/s). In low speed mode theJ-state has a differential of zero, and the K state has a differentialof 1. In high speed mode these states are reversed.

In this embodiment there are three one-way optical connections 101/311,102/312, 103/313, from the peripheral transceiver 10 to the hosttransceiver 30, and three such connections 301/111, 302/112, 304/114 inthe reverse direction. Each connection comprises an infra red LED 101,102, 103, 301, 302, 304 in one transceiver and a correspondingphotodiode 111, 112, 114, 311, 312, 313 in the other, making six opticalconnections in total.

Four of the optical connections are used to provide a pair of two-wayoptical links interrupting each data wire 191/391, 192/392 connectingthe terminal 40 to equipment 20. Two infra-red LEDs 101, 102; (301, 302)are used in each transceiver, co-operating with two photodiodes 311,312; (111, 112), which detect the signals sent by the LEDs in thecorresponding transceiver. It is feasible to use a single LED in eachtransceiver, but this requires more complex drive circuitry and thus thedual LED option is preferred.

An infra-red link can be achieved by moving the two transceivers 10, 30into alignment such that data can be transmitted between them.Disconnection can be achieved reliably by moving the transceivers 10, 30out of close alignment, such that the photodiodes 111, 112, 311, 312each detect a low logic signal, which is the USB signal for adisconnection. However, in the preferred embodiment a fifth infra redlink is provided, comprising additional pulsed light source 103 in theperipheral transceiver 10, and a corresponding detector 313 is providedin the host transceiver 30, to avoid spurious signals from ambient lightsources. The detector 313 provides an input to control logic 27controlling the operation of the host transceiver 30.

In a standard USB link the peripheral (in this case the electronicdevice 20) identifies whether it is a low-speed or high-speed device bythe presence of a resistance across one or other of the data wires 191,192, and the USB host (in this case the terminal 40) determines whetherthe peripheral is a low-speed or high-speed device by comparing thevoltages on the signalling wires 191, 192. The infra-red link isarranged to replicate this signal by arranging that the peripheraltransceiver 10 connected to the peripheral device 20 identifies theconnection 191, 192 to the which the resistor is connected, andgenerates an optical signal during an otherwise idle state of the link101, 311; 102, 312, so that the corresponding host transceiver 30 cangenerate a voltage in the signal wires 391, 392 connecting thetransceiver 30 to the terminal 40, thus replicating the conditions inthe wires 191 192 connecting the peripheral transceiver 10 to theperipheral device 20.

As previously described with reference to FIG. 4, the connectionsbetween the transceivers 10, 30 cannot be simply connected in reverseparallel, but are arranged for half-duplex operation, in other wordseach direction must be switched out of use when the other is operating.This is achieved by means of switches 121, 122, 321, 322 controlled byrespective switching units 12, 32 in the transceivers 10, 30. Theswitching unit 12 in the peripheral transceiver 10 is controlled bysignals received from the switching unit 32 in the host transceiver 30over a sixth optical link 304, 114. The fact that the system operates indifferential mode makes it possible for the control unit 32 of the hosttransceiver 30 to monitor the inputs received from the LEDs 101, 102 ofthe other transceiver 10, (as shown by monitoring points 331, 332), andif incoming data is detected on either line then the transceiver 30 isset to receive that data. The USB protocol defines token packets, andthese tokens determine the direction of the packets to follow, Inessence, if an IN packet is sent from the host 40 then it is expectingdata to be sent to it, so once the packet is completed the switches 121,122, 321, 322 can be set for the incoming data. In the same fashion, ifan OUT packet is sent then the next packets will be in the samedirection so the switches are left as they are. The default condition isarranged such that the host 30 is always allowed to transmit and theperipheral 10 to receive. When a data packet received from peripheral 10has terminated (upon detection of an EOP signal), the switches 121, 122,321, 322 are re-set to the default condition.

Operation of the connection can be over-ridden if the detector 313 failsto detect the LED 103, Such a failure, caused by separation of thetransceivers 10, 30 from each other, causes the control unit 32 toemulate a disconnection sequence .

The host terminal 40 and transceiver 30 can be incorporated into apayphone for use in public areas. The peripheral transceiver 10 can beconnected to a personal computer 20 (preferably via a USB connection 11)so that users can connect from an internet café or similar location. Theperipheral device transceiver 10 could be incorporated into theelectronic device 20 but it is thought that it is preferable for thetransceiver to be removable so that the user device 20 can be connecteddirectly to a terminal 40 through a USB cable and connector when one isavailable.

Although the preceding discussion focuses on infra-red communicationlinks, it will be understood that visible light, or radiation from thenear ultra-violet region could be also be used for the communicationslink.

1. An optical transceiver, the transceiver comprising: means enabling anassociated electronic device to transmit and receive data signals in aUSB two channel format, and a pair of transmitter means to directlymodulate the received USB two channel-format signals onto respectiveoptical carriers, and a pair of receivers to extract USB twochannel-format modulated signals from respective optical carriers.
 2. Atransceiver according to claim 1, further comprising: means fordetecting a configuration of an electronic device to which it isconnected, means for generating data in accordance with the detectedconfiguration, means for detecting an idle period in the transmitted andreceived data signals, and means for transmitting the generatedconfiguration data over the optical carriers during said idle period. 3.A transceiver according to claim 2, wherein the configuration datarelates to the data rate at which the electronic device is to operate.4. A transceiver according to claim 1, further comprising: means fordetecting an idle period in the transmitted and received data signals,means for receiving configuration data over the optical carriers duringsaid idle periods, and means for configuring the electronic deviceaccording to the configuration data.
 5. A transceiver according to claim1, further comprising transmission means for transmitting an alertsignal to a co-operating transceiver.
 6. A transceiver according toclaim 5, wherein the transmission means is a pulsed light emittingdiode.
 7. A transceiver according to claim 1, further comprising:detection means for detecting an alert signal indicative that aco-operating transceiver is present.
 8. A transceiver according to claim7, wherein the detection means comprises an optical sensor.
 9. Atransceiver according to claim 1 arranged for time division duplexoperation with a co-operating transceiver.
 10. A transceiver accordingto claim 9, further comprising: means for transmitting a control signalfor controlling operation of a co-operating transceiver, means foroperating in receive mode for a predetermined period after transmissionof the control signal, means for detecting signals received from theco-operating transceiver, and means for switching to transmit mode if nosuch signals are detected.
 11. A transceiver according to claim 1,further comprising: means for connection to and disconnection from anassociated electronic device.
 12. A transceiver according to claim 11,wherein the connection is a wired connection operable in USB format. 13.A transceiver according to claim 1 wherein the optical transceiver isincorporated in a docking port for connection to a complementary dockingport having a corresponding transceiver, the docking ports havingalignment means arranged such that plural optical interfaces in onetransceiver are aligned with respectively corresponding plural opticalinterfaces in a corresponding further transceiver so as to minimizeinterference between corresponding plural optical communicationchannels, and from external light sources.
 14. An optical transceiver,the receiver comprising: means enabling an associated electronic deviceto transmit and receive data signals in a USB two channel format, andmeans to directly modulate the received USB-format signals onto a pairof optical carriers, and to extract USB two channel-format modulatedsignals from a pair of optical carriers, said transceiver being arrangedfor time division duplex operation with a co-operating transceiver;detection means for detecting a control signal from a co-operatingtransceiver, and means for putting the transceiver into transmit mode inresponse to the control signal.
 15. An optical transceiver, thetransceiver comprising: means enabling an associated electronic deviceto transmit and receive data signals in a USB two channel format, andmeans to directly modulate the received USB-format signals onto anoptical carrier, and to extract USB-format modulated signals from anoptical carrier; transmission means for transmitting an alert signal toa cooperating transceiver; wherein the transmission means comprises apulsed light emitting diode; three pairs of optical transmitters andsensors, wherein two of the pairs are used for duplex operation in thetwo-channel USB format, and the third pair is used for exchange of thealert and control signals.
 16. A communications terminal, the terminalcomprising: a transceiver according to claim 1 and the associatedelectronic device.
 17. A communications terminal according to claim 16,connected to a storage device by a communications network.
 18. Acommunications terminal according to claim 16, further comprising meansfor processing payment for use of the terminal.
 19. A communicationsterminal as in claim 16 wherein the optical transceiver is incorporatedin a docking port for connection to a complementary docking port havinga corresponding transceiver associated with alignment means arrangedsuch that plural optical interfaces in one transceiver are aligned withrespectively corresponding plural optical interfaces in a correspondingfurther transceiver so as to minimize interference between correspondingplural optical communication channels, and from external light sources.20. A method for coupling a USB port of a first electronic device to aUSB channel of a second electronic device via an optical communicationslink, said method comprising: enabling an electronic device to eachtransmit and receive data signals in a USB two channel format by (a)modulating USB two channel-format signals onto a pair of opticalcarriers and (b) by extracting USB two channel-format modulated signalsfrom a pair of optical carriers.
 21. A method as in claim 20 furthercomprising harmonizing configurations of two coupled devices on the sameUSB data rate by: detecting a configuration of a connected electronicdevice, generating data in accordance with the detected configuration,detecting an idle period in the transmitted and received data signals,and transmitting the generated configuration data over the opticalcarriers during said idle period.
 22. A method as in claim 21 whereinthe configuration data relates to the data rate at which the electronicdevice is to operate.
 23. A method as in claim 20 further comprisingharmonizing configurations of two coupled devices on the same USB datarate by: detecting an idle period in the transmitted and received datasignals, receiving configuration data over the optical carriers duringsaid idle periods, and configuring an electronic device according to theconfiguration data.
 24. A method as in claim 20 further comprisingtransmitting an alert signal to a co-operating transceiver.
 25. A methodas in claim 20 further comprising: detecting an alert signal indicativethat a co-operating transceiver is present.
 26. A method as in claim 20using time division duplex operation with a co-operating transceiver.27. A method as in claim 26 further comprising synchronizing duplexoperation of the USB signals by: transmitting a control signal forcontrolling operation of a co-operating transceiver, operating inreceiving mode for a predetermined period after transmission of thecontrol signal, detecting signals received from the co-operatingtransceiver, and switching to transmit mode if no such signals aredetected.
 28. A method as in claim 26 further comprising synchronizingduplex operation of the USB signals by: detecting a control signal froma co-operating transceiver, and putting the transceiver into transmitmode in response to the control signal.
 29. A method as in claim 20further comprising: incorporating said optical link in a docking portfor connection to a complementary docking port having a correspondingtransceiver associated with alignment means arranged such that pluraloptical interfaces in one transceiver are aligned with respectivelycorresponding plural optical interfaces in a corresponding furthertransceiver so as to minimize interference between corresponding pluraloptical communication channels, and from external light sources.
 30. Amethod as in claim 20 further comprising connecting an optically linkedelectronic device to a storage device via communications network.
 31. Amethod as in claim 20 further comprising: processing payment for use ofone of said electronic devices operating as a terminal for connection toa communications network.
 32. A method for coupling a USB port of afirst electronic device to a USB channel of a second electronic devicevia an optical communications link, said method comprising: enabling anelectronic device to each transmit and receive data signals in a USB twochannel format by (a) modulating USB-format signals onto an opticalcarrier and (b) by extracting USB-format modulated signals from anoptical carrier; using three pairs of optical transmitters and sensors,wherein two of the pairs are used for duplex operation in thetwo-channel USB format, and the third pair is used for exchange of alertand control signals.